Sudden cardiac death afflicts approximately 300,000 people in the United States every year, and is one of the most pressing health problems in the world (R. Myerburg et al., Circulation 85, 1-10 (1992)). Most sudden cardiac deaths are caused by malignant ventricular arrhythmias. Malignant ventricular arrhythmias which lead to death are often triggered by emotional changes, especially stress and fear, during myocardial ischemia and infarction.
Historically, the hypothalamus has been credited with the major control of cardiovascular responses associated with emotions, stress, and defense in both humans and animals. Karplus and Kreidl first demonstrated that electric stimulation of the hypothalamus can cause discharges in many portions of the sympathetic nervous system (J. Karplus and A. Kreidl, Pflugers Archiv. 129, 138 (1909)). Stimulation of the hypothalamus can induce tachyarrhythmias in both normal and ischemic animal ventricles (see, e.g., C. Carpeggiani et al., Circ. Res. 70, 600 (1992); J. Skinner and J. Reed, Am. J. Physiol. 240, H156 (1981)). The activities of the cardiovascular centers in the brain can be modulated by afferent nerve stimulation (see, e.g., L. Renaud et al., Brain Res. Bull. 20, 771 (1988); X. Ying et al., Acta Physiol. Sinica 36, 133 (1984)). A few reports suggest that stimulation of afferent nerves can reduce the arrhythmias induced by hypothalamic stimulation in normal rabbits (Y. Xia et al., J. Tradit. chin. Med. 7, 211 (1987); Y. Xia et al., J. Acupunc. Electro-therap. Res. 11, 191 (1986)). However, there is a continued need for new methods and implantable apparatus for preventing arrhythmia before it occurs, and for treating such arrhythmia in the event that prevention is ineffective.